1. Field of the Invention
This invention generally relates to an ink-jet printer, and, in particular, to an ink-jet printer head for use in ink-jet printers.
2. Description of the Prior Art
As shown in FIGS. 1 and 2, the so-called on-demand type ink-jet printer head for producing printing ink droplets on the basis of volume displacement is well known in the art, as disclosed in U.S. Pat. No. 3,946,398. The on-demand type printer head includes a main body or base plate 5, in which are defined a pressure chamber 2 and inlet and outlet passages 4a, 4b, and a top cover plate 6 provided with a hole corresponding in position to the pressure chamber 2. A pusher unit 3 comprised of a piezoelectric plate and a support plate for supporting thereon the piezoelectric plate is provided with its periphery fixed to the edge of the hole of the top cover plate 6 thereby forming a ceiling of the pressure chamber 2. An ink inlet pipe 7 is fixedly provided in fluidic communication with the ink inlet passage 4a and an ink supply tube 8 is sealingly fitted onto the mouth end of the ink inlet pipe 7. Although not shown specifically, the other end of the ink supply tube 8 is connected to an ink reservoir. A nozzle opening 1 is defined at the end of the outlet passage 4b opposite to the pressure chamber 2, and, thus, when the pusher unit 3 is deflected downward in response to a print signal applied thereto, the volume of the pressure chamber 2 is reduced therby causing the ink inside of the pressure chamber and thus the ink inside of the ink outlet passage 4b is pushed out into the air through the nozzle opening 1 thereby forming an ink droplet to be used in printing. As a characteristic of such a prior art ink-jet printer head, the ink droplets are formed by volume displacement and they are not deliberately charged, which allows to make the overall structure simpler.
However, since the periphery of the pusher unit 3 is fixedly attached to the edge or sidewall of the hole provided in the top cover plate 6, the pusher unit 3 must be made relatively large areawise in order to obtain a sufficient amount of deflection. This is particularly disadvantageous in the case of forming a multi-nozzle structure because the spacing between the two adjacent nozzles or nozzle openings tends to be large thereby limiting density or integration, which, in turn, results in poor resolution. Such a disadvantage mainly stems from the fact that the pusher unit 3 is so provided with its periphery all fixedly attached. This may be easily understood when reference is made to FIG. 3 which illustrates the structure of a multi-nozzle head constructed in accordance with the prior art concept. In FIG. 3, only three pressure chambers 2a-2c branching out the common ink supply passage 10 are shown for the purpose of illustration.
On the other hand, another structure similar to the above-mentioned on-demand type ink-jet printer head for ejecting non-charged ink droplets by volume displacement has been proposed as disclosed, for example, in Japanese Patent Publication, No. 53-45698 and also in Japanese Patent Laid-open Publication, No. 57-24262. In this approach, a pusher unit has been proposed to dispose at the location opposite to the nozzle opening thereby ejecting ink droplets in the direction of deflection of the pusher unit. However, this structure also suffers from the above-described disadvantages. That is, the pressure chamber is relatively large and the overall structure is rather complex, which tends to make a high density multi-nozzle structure difficult.